Process for preparing relief images using acid-curable resins and masked curing catalysts

ABSTRACT

Compounds of the formula I and II ##STR1## in which R 1 , R 2 , R 3 , R 4 , R 5  and R 6 , X, Y and n are as defined in claim 1, are latent curing catalysts for preparing relief images with acid-curable resins. They are distinguished by satisfactory solubility in the acid-curable resin systems, can be stored virtually indefinitely in the dark and, when exposed to shortwave light, make it possible to cure the resins by acid catalysis at a relatively low temperature.

This is a continuation-in-part of application Ser. No. 682,451, filedDec. 17, 1984, now U.S. Pat. No. 4,636,575, issued Jan. 13, 1987, whichis a division of application Ser. No. 455,173, filed Jan. 3, 1983, nowU.S. Pat. No. 4,510,290 issued Apr. 9, 1985.

The invention relates to compositions based on an acid-curable resin andcontaining a masked curing catalyst and to a process for curing thisresin by irradiation with shortwave light, followed by warming.

Acid-curable resins are used, in particular, as binders for lacquers,printing inks and paints, if high stoving temperatures are to beavoided. Acid-curable resins can be amino resins, melamine resins,ureaformaldehyde resins, phenol-formaldehyde resins and mixtures of suchresins with alkyd, polyester or acrylic resins. Further acid-curableresins are methylol compounds, methylol ethers of polycarboxylic acidimides, for example derivatives of polyacrylic or methacrylic acid,urethane alkyds and resins containing carboxylic acid esters ofN-methylolimides. The acid curing catalysts used are mainly organicacids including, for example, sulfonic acids, in particularp-toluenesulfonic acid. Since these acids result in a slow curing attemperatures as low as room temperature, they are not added to the resinuntil shortly before the application of the latter, a procedure which isassociated with the known problems of observing specific pot lives. Inorder, therefore, to make one-component systems possible, the use ofmasked curing catalysts from which the acid is released at elevatedtemperature, has already been suggested. Examples of these are aminesalts of aromatic sulfonic acids, such as the pyridine salts suggestedin U.S. Patent Specification 3,474,054. These have the disadvantage thatthey result in a slow curing even during storage. In addition, problemsof odour arise with these products.

The suggestion has also been made, to use masked curing catalysts fromwhich the actual curing catalyst is formed by irradiation with UV light.Examples of these are aromatic sulfonium salts of complex anions, suchas are described in U.S. patent specification 4,102,687. However,sulfonium salts of this type are difficult to prepare in a pure form,they have a low reactivity and they tend to cause yellowing of theresins. Acting in accordance with the same principle, photolabilesulfonic acid esters have already been suggested, for example sulfonicacid esters of α-hydroxymethylbenzoin, such as are described, forexample in German Offenlegungsschrift No. 1,919,678. However, thesecompounds do not meet, in every respect, the requirements set for them,for example satisfactory solubility in the acid-curable resin systems,no yellowing of the resins after curing and no adverse effect onlacquering by the electrophoretic application process.

It has now been found that sulfonic acid esters of certainα-hydroxycarbonyl compounds, which are easy to prepare on an industrialscale, meet these requirements, since they can be stored in the darkvirtually indefinitely, but rapidly decompose when exposed to shortwavelight, which makes it possible subsequently to cure the resins at arelatively low temperature by acid catalysis and does not result inyellowing of the resins.

The invention relates to a curable composition containing anacid-curable resin and, as a masked curing catalyst, a compound of theformula I or II ##STR2## in which n is the number 1 or 2 and R₁ isphenyl or naphthyl which is unsubstituted or substituted, for example,by 1, 2 or 3 radicals belonging to the group comprising --Cl, --Br,--CN, --NO₂, C₁ -C₁₂ -alkyl, C₁ -C₄ -alKoxy, phenoxy, tolyloxy,phentthio, tolylthio, C₁ -C₈ -alkylthio, --SCH₂ CH₂ OH, C₁ -C₄-alkylsulfonyl, phenylsulfonyl, C₂ -C₄ -alkoxycarbonyl, C₁ -C₄-alkylamino, C₂ -C₄ -dialkylamino, phenyl--CONH--, C₁ -C₄ -alkyl--CONH--or benzoyl, or R₁ is also anthryl, phenanthryl, thienyl, pyridyl, furyl,indolyl or tetrahydronaphthyl, and R₂ is hydrogen or C₁ -C₈ -alkyl whichis unsubstituted or substituted, for example, by --OH, --Cl, C₁ -C₄-alkoxy, --CN, C₂ -C₅ -alkoxycarbonyl, phenyl, chlorophenyl, C₇ -C₁₀-alkylphenyl or C₇ -C₁₀ -alkoxyphenyl, or is also benzoyl, R₃ is asdefined for R₂ and is also phenyl which is unsubstituted or substituted,for example, by --Cl, C₁ -C₄ -alkyl, C₁ -C₄ -alkoxy or C₁ -C₄-alkylthio, C₂ -C₈ alkoxycarbonyl, --CN, C₁ -C₄ -alkyl--NH--CO--,phenyl--NH--CO-- or --CONH₂, or R₂ and R₃, together with the carbon atomto which they are attached, constitute a C₄ -C₆ -cycloalkyl ring, X is--0--, --S--, --SO₂ --, --CH₂ --, --C(CH₃)₂ -- or >N--COR₇, R₇ being C₁-C₄ -alkyl or phenyl, and Y is a direct bond or --CH₂ --, and, if n=1,R₄ is C₁ -C₁₈ -alkyl, phenyl which is unsubstituted or substituted, forexample, by halogen, C₁ -C₁₂ -alkyl, C₁ -C₄ -alkoxy, C₁ -C₄-alkyl--CONH--, phenyl--CONH--, --NO₂ or benzoyl, naphthyl which isunsubstituted or substituted, for example, by halogen, C₁ -C₁₂ -alkyl orC₁ -C₄ -alkoxy, C₅ -C₆ -cycloalkyl, C₇ -C₉ -aralkyl, camphoryl, --CF₃,--CCl₃, --F or --NH₂, and, if n=2, R₄ is a --(CH₂)_(m) -- group in whichm is the number 2 to 8, or R₄ is phenylene or napthylene which isunsubstituted or substituted, for example, by C₁ -C₁₂ -alkyl, R₅ is Hor, for example, 1, 2 or 3 radicals belonging to the group comprising--Cl, --Br, --NO.sub. 2, C₁ -C₁₂ -alkyl, C₁ -C₄ -alkoxy, phenoxy,phenylthio, C₁ -C₈ -alkylthio or --SCH₂ CH₂ OH, and R₆ is hydrogen or C₁-C₈ -alkyl which is unsubstituted or substituted, for example, by --OH,--Cl, C₁ -C₄ -alkoxy, --CN, C₂ -C₅ -alkoxycarbonyl, phenyl,chlorophenyl, C₇ -C₁₀ -alkylphenyl or C₇ -C₁₀ -alkoxyphenyl, phenylwhich is unsubstituted or substituted, for example, by --Cl, C₁ -C₄-alkyl, C₁ -C₄ -alkoxy or C₁ -C₄ -alkylthio, C₂ -C₈ alkoxycarbonyl or--CN.

C₁ -C₁₂ -alkyl substituents in phenyl or naphthyl, as R₁, are linear orbranched substituents, for example methyl, ethyl, n-propyl, isopropyl,n-butyl, sec.-butyl, tert.-butyl, pentyl, hexyl, heptyl, octyl, nonyl,decyl, undecyl or dodecyl, but particularly methyl. C₁ -C₄ -alkoxysubstituents in phenyl or naphthyl, as R₁, are, for example, methoxy,ethoxy, propoxy or tert.-butoxy.

C₁ -C₈ -alkylthio substituents in phenyl or naphthyl, as R₁, and in R₅are linear or branched substituents, for example methylthio, ethylthio,n-propylthio, isopropylthio, n-butylthio, sec.-butylthio,tert.butylthio, pentylthio, hexylthio, heptylthio or octylthio, butparticularly methylthio.

A C₁ -C₄ -alkylamino or C₂ -C₄ -dialkylamino substituent in phenyl ornaphthyl, as R₁, is, for example, a methylamino, ethylamino, propylaminoor n-butylamino substituent group or a dimethylamino or diethylaminosubstituent group, respectively.

A C₁ -C₄ -alkylsulfonyl substituent in phenyl or naphthyl, as R₁, is,for example, methylsulfonyl, ethylsulfonyl, propylsulfonyl,butylsulfonyl or tert.butylsulfonyl.

A C₁ -C₄ -alkyl--CONH-- substituent in phenyl or naphthyl, as R₁, is,for example, methyl--CONH--, ethyl--CONH--, propyl--CONH-- orn-butyl--CONH--. C₁ -C₄ -alkyl--NHCO-- present in R₂ or R₃, and C₁ -C₄-alkyl--CONH-- present in R₄ are, for example, respectively,methyl--NHCO--, ethyl--NHCO--, propyl--NHCO-- or n-butyl--NHCO--substituents or methyl--CONH--, ethyl--CONH--, propyl--CONH-- orn-butyl--CONH-- substituents.

All the position isomers of thienyl, pyridyl, furyl, indolyl ortetrahydronaphthyl, as R₁, are suitable. However, preferred positionisomers are 2-thienyl, 3-pyridyl, 2-furyl, 3-indolyl or1,2,3,4-tetrahydro-6-naphthyl.

As C₁ -C₈ -alkyl, R₂, R₃ and R₆ are linear or branched alkyl groups, butpreferably linear C₁ -C₄ -alkyl groups, for example methyl, ethyl,n-propyl or n-butyl.

C₁ -C₄ -alkoxy substituents in C₁ -C₈ -alkyl, as R₂, R₃ and R₆, or inphenyl or naphthyl, as R₄ or R₅, are, for example, methoxy, ethoxy,propoxy or tert.butoxy substituents.

C₇ -C₁₀ -alkylphenyl or C₇ -C₁₀ -alkoxyphenyl substituents in C₁ -C₈-alkyl, as R₂, R₃ and R₆, are, for example, methylphenyl, methoxyphenyl,ethylphenyl, ethoxyphenyl, tert.-butylphenyl or tert.-butoxy-phenyl.

C₁ -C₄ -alkylthio substituents in phenyl, as R₃ and R₆, are, forexample, methylthio, ethylthio, propylthio or tert.-butylthio.

A cycloalkyl ring which is formed by R₂ and R₃, together with the C atomto which they are attached, is, for example, a cyclopentane, cyclohexaneor cycloheptane ring, but particularly a cyclohexane ring.

If n=1: C₁ -C₁₈ -alkyl which is represented by R₄ is a linear orbranched group, for example methyl, ethyl, propyl, isopropyl, butyl,tert.-butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, 2-ethylhexyl,undecyl, dodecyl, tert.-dodecyl, tridecyl, tetradecyl, hexadecyl oroctadecyl.

C₁ -C₁₂ -alkyl substituents in phenyl or naphthyl, as R₄, and in R₅ arelinear or branched alkyl groups.

C₅ -C₆ -cycloalkyl which is represented by R₄ is cyclopentyl andcyclohexyl.

C₇ -C₉ -aralkyl which is represented by R₄ is, for example,1-phenylethyl, 2-phenylethyl or benzyl.

Camphoryl as R₄ is 10-camphoryl.

If n=2: a --(CH₂)_(m) -- group which is represented by R₄ is, forexample, ethylene, propylene, butylene, pentylene or hexamethylene.

C₁ -C₁₂ -alkyl substituents in phenylene or naphthylene are linear orbranched alkyl groups.

If the various phenyl groups in the radicals R₁, R₃, R₄ and R₆ aresubstituted by radicals other than hydrogen atoms, this substitutiontakes place in the ortho-, meta- or para-position, but particularly inthe para-position.

Preferred curing catalysts are those of the formula I wherein n is thenumber 1 or 2, R₁ is phenyl or naphthyl which is unsubstituted or issubstituted, for example, by --Cl, --Br, C₁ -C₈ -alkyl, C₁ -C₄ -alkoxy,phenoxy, tolyloxy, phenylthio, tolylthio, --SCH₂ CH₂ OH, C₁ -C₈-alkylthio or benzoyl, or is anthryl or phenanthryl, R₂ is hydrogen orC₁ -C₈ -alkyl which is unsubstituted or is substituted, for example, by--OH, --Cl, --CN, C₂ -C₅ -alkoxycarbonyl, phenyl, chlorophenyl, C₇ -C₁₀alkylphenyl or C₇ -C₁₀ -alkoxyphenyl and R₃ is the same as R₂, asdefined above, and is also phenyl which is unsubstituted or issubstituted, for example, by --Cl, C₁ -C₄ -alkyl, C₁ -C₄ -alkoxy or C₁-C₄ -alkylthio, or is C₂ -C₄ -alkoxycarbonyl or --CN, or R₂ and R₃,together with the carbon atom to which they are attached, form a C₄ -C₆-cycloalkyl ring and, if n=1, R₄ is C₁ -C₁₈ -alkyl, phenyl which isunsubstituted or is substituted, for example, by --Cl, C₁ -C₁₂ -alkyl orC₁ -C₄ -alkoxy, or is naphthyl which is unsubstituted or is substituted,for example, by --Cl or C₁ -C₁₂ -alkyl, or R₄ is also camphoryl, --CF₃or --F, and, if n=2, R₄ is a --(CH₂)_(m) group, phenylene ornaphthylene, m being the number 2, 3 or 4.

Particularly preferred curing catalysts are those of the formula I inwhich n=1 and R₁ is phenyl which is unsubstituted or is substituted, forexample, by chlorine, methyl, methoxy, methylthio, phenylthio, --SCH₂CH₂ OH or benzoyl, R₂ is hydrogen or C₁ -C₄ -alkyl, R₃ is hydrogen, C₁-C₄ -alkyl or phenyl, or R₂ and R₃, together with the carbon atom towhich they are attached, form a cyclohexane ring and R₄ is C₁ -C₁₈-alkyl, unsubstituted phenyl or naphthyl, or camphoryl.

Curing catalysts which are very particularly preferred are those of theformula I in which n=1, R₁ is phenyl, p-tolyl or p-methylthiophenyl, R₂is hydrogen, R₃ is methyl, isopropyl, n-decyl or benzyl and R₄ isphenyl, p-tolyl or p-n-dodecylphenyl.

Curing catalysts which are also particularly preferred are those of theformula II in which n=1, R₅ and R₆ are hydrogen, X and Y are a --CH₂ --group and R₄ is C₁ -C₁₈ -alkyl, phenyl or naphthyl which isunsubstituted or is substituted, for example, by C₁ -C₁₂ -alkyl, or iscamphoryl.

The following are examples of individual compounds of the formula I:2-[(p-tolylsulfonyl)-oxy]-1-phenyl-1-propanone,2-[(p-tolylsulfonyl)-oxy]-1-p-tolyl-1-propanone,2-[(p-chlorophenylsulfonyl)-oxy]-1-phenyl-1-propanone,2-[(p-laurylphenylsulfonyl)-oxy]-1-phenyl-1-propanone,2-[(p-methoxyphenylsulfonyl)-oxy]-1-phenyl-1-propanone,2-[(p-methylthiophenylsulfonyl)-oxy]-1-phenyl-1-propanone,2-[(p-acetamidophenylsulfonyl)-oxy]-1-phenyl-1-propanone,2-[(methylsulfonyl)-oxy]-1-phenyl-1-propanone, benzoin toluenesulfonate,benzoin methanesulfonate, benzoin p-dodecylbenzenesulfonate,4,4'-bis-methylthiobenzoin toluenesulfonate,2-[(o-nitrophenylsulfonyl)-oxy]-1-phenyl-1-propanone,2-[(benzylsulfonyl)-oxy]-1-phenyl-1-propanone,2-[(n-octylsulfonyl)-oxy]-1-phenyl-1-propanone,2-[(cyclohexylsulfonyl)-oxy]-1-phenyl-1-propanone,2-[(phenylsulfonyl)-oxy]-1-phenyl-1-propanone, 2-[(-naphthylsulfonyl)-oxy]-1-phenyl-1-propanone,2-[(trifluoromethylsulfonyl)-oxy]-1-phenyl-1-propanone, 2-[(-chloroethylsulfonyl)-oxy]-1-phenyl-1-propanone,2-[(mesitylsulfonyl)-oxy]-1-phenyl-1-propanone,2-[(10'-camphorylsulfonyl)-oxy]-1-phenyl-1-propanone,1-benzoyl-1-methylsulfonyloxy-cyclohexane, 2-[(p-tolylsulfonyl)-oxy]-1-(2'-thienyl)-1-propanone,2-[(methylsulfonyl)-oxy]-1-(6'-tetralin)-1-propanone,2-[(p-tolylsulfonyl)-oxy]-1-phenyl- 1-octanone,2-[(p-tolylsulfonyl)-oxy]-1-phenyl-1-dodecanone,2-[(p-tolylsulfonyl)-oxy)-1-p-tolyl-1-dodecanone,2-](methylsulfonyl)-oxy[-4-ethoxycarbonyl-1-phenyl- 1-butanone,2-](p-tolylsulfonyl)-oxy[-acetophenone,2-](p-tolylsulfonyl)-oxy[-2-methyl-1-phenyl-1-propanone,2-](10'-camphorylsulfonyl)-oxy[-acetophenone,2-(10'-camphorylsulfonyl)-oxy]-2-methyl-1-(p-methyl)-phenyl-1-propanone,2-[(10'-camphorylsulfonyl)-oxy]-2-methyl-1-(p-methylthio)-phenyl-1-propanone,2-[(10'-camphorylsulfonyl)-oxy]-1-p-(-hydroxyethylthio)-phenyl-1-propanone,2-[(10'-camphorylsulfonyl)-oxy]-1-(p-chloro)-phenyl- 1-propanone,2-[(p-tolylsulfonyl)-oxy]-1,3-bis-phenyl-1-propanone,2-[(methylsulfonyl)-oxy]-1,3-bis-phenyl-1-propanone,2-[(p-tolylsulfonyl)-oxy]-3-phenyl-1-p-tolyl-1-propanone,2-[(p-laurylphenylsulfonyl)-oxy]-1,3-bis-phenyl-1-propanone,2-[(p-tolylsulfonyl)-oxy]-2-methoxymethyl-1-phenyl-1-propanone,2-[(methylsulfonyl)oxy]-2-chloromethyl-1-phenyl-1-propanone,2-[(p-tolylsulfonyl)-oxy]-p-methylthioacetophenone,2-[(methylsulfonyl)-oxy]-1-(p-methylthio)-phenyl-1-propanone,2-[(p-tolylsulfonyl)-oxy]-1-(p-methylthio)-phenyl-1-propanone,2-[(p-laurylphenylsulfonyl)-oxy]-1-(p-methylthio)-phenyl-1-propanone,2-[(p-tolylsulfonyl)-oxy]-3-phenyl-1-(p-methylthio)-phenyl-1-propanone,2-[(p-tolylsulfonyl)oxy]-1-(p-phenylthio)-phenyl-1-propanone,2-[(p-tolylsulfonyl)-oxy]-1-(p-acetamido)-phenyl-1-propanone,2-[(p-laurylphenylsulfonyl)-oxy]-3-methyl-1-p-methylthiophenyl-1-butanone,2-[(p-tolylsulfonyl)-oxy]-3-methyl-1-phenyl-1-butanone,2-[(p-tolylsulfonyl)-oxy]-3-methyl-1-p-tolyl-1-butanone,2-[(p-tolylsulfonyl)-oxy]-1- -naphthyl-1-propanone,2-[(p-tolylsulfonyl)-oxy]-2-ethoxycarbonylacetophenone, diethyl3-[(p-tolylsulfonyl)-oxy]-3-benzoylmalonate, (1'-benzoyl)-ethylphthalic-anhydride-5-sulfonate, (1'-methyl-1'-benzoyl)-ethylN-methylphthalimide-5-sulfonate, bis-( 1'-benzoyl)-ethylnaphthalene-2,6-disulfonate and bis-(1'-benzoyl-1'-methyl)-ethyldinonylnaphthalenedisulfonate.

The following are examples of individual compounds of the formula II:2-[(methylsulfonyl)-oxy]-2-methyltetral-1-one,2-[(methylsulfonyl)-oxy]-tetral-1-one,2-[(p-tolylsulfonyl)-oxy]-tetral-1-one,2-[(p-laurylphenylsulfonyl)-oxy]tetral-1-one,3-[(p-tolylsulfonyl)oxy]-chromone,3-[(p-tolylsulfonyl)-oxy]-1-thiochroman-4-one,3-[(camphorylsulfonyl)-oxy]-1-thiochroman-4-one-S-dioxide,2-[(methylsulfonyl)-oxy]-coumaran-3-one and2-[(phenylsulfonyl)-oxy]-indan-1-one. Many compounds of the formula Iare known and can be prepared by known processes, for example byreacting the corresponding hydroxy compounds of the formula III ##STR3##with one equivalent or with half an equivalent of the correspondingmonosulfonyl or disulfonyl chlorides, respectively, of the formula IV

    R.sub.4 (SO.sub.2 Cl).sub.n                                IV

in the presence of a base [in this connection see Journal of theChemical Society, Perkin I, 1981, page 263 or Journal of Org. Chem 34,1,595 (1969)], or by reacting the corresponding bromine derivatives ofthe formula V ##STR4## with one equivalent or with half an equivalent ofthe silver salts of the corresponding monosulfonic or disulfonic acidderivatives, respectively, of the formula VI

    (AgO.sub.3 S).sub.n R.sub.4                                VI

for example by the process described in the Journal of Organic Chemistryof the USSR, volume 8, page 2,166 (1972), or, for a specific class ofthese compounds, by the direct reaction between an acetophenone of theformula VII and the iodonium salt of the formula VIII, giving thecorresponding product of the formula IX ##STR5## for example by theprocess described in the Journal of Org. Chem., 47, 2,487 (1982).

In the formulae III, IV, V and VI, VII and IX, the radicals R₁ to R₄ andn are as defined above.

Other compounds of the formula I, and also the compounds of the formulaII, are novel and therefore also form a subject of the presentinvention. They are prepared analogously to the known compounds.

The novel compounds of the formula I have the formula X ##STR6## inwhich n is the number 1 or 2 and R₈ is phenyl or naphthyl which issubstituted, for example, by C₂ -C₁₂ -alkyl, C₂ -C₄ -alkoxy, phenoxy,tolyloxy, phenylthio, tolylthio, C₁ -C₈ -alkylthio, --SCH₂ -CH₂ OH, C₁-C₄ alkylsulfonyl, phenylsulfonyl, C₁ -C₄ -alkylamino, C₂ -C₄-dialkylamino, phenyl--CONH--, C₁ -C₄ -alkyl--CONH-- or benzoyl, or R₈is also anthryl, phenanthryl, thienyl, pyridyl, furyl, indolyl ortetrahydronaphthyl, R₉ is C₂ -C₈ -alkyl or C₁ -C₈ -alkyl which issubstituted, for example, by --OH, --Cl, C₁ -C₄ -alkoxy, --CN, C₂ -C₅-alkoxycarbonyl, phenyl, chlorophenyl, C₇ -C₁₀ -alkylphenyl or C₇ -C₁₀-alkoxyphenyl, R₁₀ is as defined for R₉ and is also phenyl which issubstituted by --Cl, C₁ -C₄ -alkyl, C₁ -C₄ -alkoxy or C₁ -C₄ -alkylthio,C₄ -C₈ -alkoxycarbonyl, --CN, C₁ -C₄ -alkyl--NHCO--, phenyl--NHCO-- or--CONH₂, or R₉ and R₁₀, together with the carbon atom to which they areattached, form a C₄ -C₆ -cycloalkyl ring, and, if n=1, R₁₁ is C₂ -C₁₈-alkyl, phenyl which is substituted, for example, by C₂ -C₁₂ -alkyl, C₂-C₄ -alkoxy, C₁ -C₄ -alkyl--CONH--, phenyl--CONH-- or benzoyl, naphthylwhich is unsubstituted or is substituted, for example, by halogen, C₁-C₁₂ -alkyl or C₁ -C₄ -alkoxy, C₅ -C₆ -cycloalkyl, C₇ -C₉ -aralkyl,camphoryl, --CF₃, -CCl₃, --F or --NH₂, and, if n=2, R₁₁ is a --(CH₂)_(m)--group in which m is the number 2 to 8, or R₁₁ is pheny-lene ornaphthylene which is unsubstituted or is sub-stituted, for example, byC₁ -C₁₂ -alkyl.

Many intermediates of the formula III, IV, V, VI and VII are knowncompounds which can be prepared by known processes, for example by theprocesses which are described in Houben-Weyl, Methoden der organischenChemie ("Methods of Organic Chemistry"): volume V/4, pages 171 to 189,for the compounds of the formula V, volume IX, pages 411 and 563, forthe compounds of the formula IV, and, for the compounds of the formulaIII, the literature references A. 526, 143, 164 (1936), Am. Soc. 76,4,402 (1954) or Z. obsc. Chim. 34, 3,165 (1964). Other intermediates ofthe formula III, IV, V, VI and VII are novel and therefore also form asubject of the present invention. They are prepared analogously to theknown compounds.

The curing catalysts according to the invention are added to the resinsin an amount which is adequate for curing. The amount required dependsnot only on the nature of the resin but also on the intended curingtemperature and curing time. In general, 0.1 to 10% by weight,preferably 0.5 to 5% by weight, based on the solvent-free resin, areused. It is also possible to employ mixtures of the curing catalystsaccording to the invention.

Suitable acid-curing resins are any resins, the curing of which can beaccelerated by acid catalysts. These are, in particular, lacquers basedon acrylic, polyester, alkyd, melamine, urea and phenolic resins, butespecially mixtures of acrylic, polyester or alkyd resins with oneanother or with a melamine resin. These also include modified lacquerresins, for example acrylicmodified polyester or alkyd resins. Examplesof various types of resins which are included under the term acrylic,polyester and alkyd resins are described, for example, in Wagner,Sarx/Lackkunstharze ("Synthetic Resins for Paints") (Munich, 1971),pages 86 to 123 and 229 to 238, or in Ullmann/Encyclopadie der techn.Chemie ("Ullmann's Encyclopedia of Industrial Chemistry"), 4th edition,volume 15 (1978), pages 613 to 628. Acid catalysis is particularlyimportant for curing lacquers containing etherified amino resins, forexample methylated or butylated melamine resins (N-methoxymethylmelamineor N-butoxymethylmelamine or methylated]butylated glycolurils and thelike), for example: ##STR7##

Further resin compositions are mixtures of polyfunctional alcohols oraryl and polyester resins containing hydroxyl groups, or partiallysaponified polyvinyl acetate or polyvinyl alcohol containingpolyfunctional dihydropyranyl ethers, for example derivatives of3,4-dihydro-2H-pyran-2-carboxylic acid.

Resin compositions containing monomeric or oligomeric constituentshaving polymerisable, unsaturated groups are also used for specificpurposes. Resin compositions of this type can also be cured by theprocess according to the invention. In this process it is possible touse concomitantly, in addition, free-radical polymerisation initiatorsor photo-initiators, for example those belonging to the category ofaromatic ketones, benzoin compounds, benzylketals orα-hydroxyacetophenone derivatives, or the compounds of the formulae I orII. The former initiate the polymerisation of the unsaturated groupsduring heat treatment and the latter during UV irradiation. In certaincases it is also possible to add H-donors. Resin compositions of thistype containing unsaturated components can also be polymerised byelectron radiation. However, in addition to the polymerisation of theunsaturated components, an acidcatalysed crosslinking must always becarried out (if necessary during stoving).

The lacquers can be solutions or dispersions of the lacquer resin in anorganic solvent or in water, but they can also be solvent-free. Lacquershaving a low proportion of solvent, so-called "high-solids lacquers" areof particular interest. The lacquers can be clear lacquers, such as areused, for example in the automobile industry, as top lacquers ofmulti-layer coatings. They can also contain pigments, both inorganic ororganic pigments, and also metal powders for metallic effect lacquers.

The following compositions according to the invention constitute furtherspecial preferred forms of the invention:

(a) A composition which, as an acid-curable resin, is an amino resin ora mixture of an amino resin with another acid-curable resin.

(b) A composition which, as the acid-curable resin, contains a phenolicresin or a mixture of such a resin with another acid-curable resin.

(c) A composition which, as the resin, contains a mixture of at leastone polymerisable compound having one or more polymerisable,ethylenically unsaturated bonds, and at least one aminoplast, such as amelamine resin or a urea-aldehyde resin, and, in addition, containsfree-radical polymerisation initiators and, if desired,photo-initiators.

Examples of polymerisable compounds having one or more polymerisable,ethylenically unsaturated bonds are esters of acrylic and methacrylicacid, hydroxyethyl esters of acrylic and methacrylic acid, diacrylatesand polyacrylates and also dimethacrylates and polymethacrylates ofglycols and polyols, aromatic vinyl and divinyl derivatives, N-methylolderivatives of acrylamide or methacrylamide, vinyl alkyl ethers,trimethylolpropane diallyl ether mono-(meth)acrylates, reaction productsof glycidyl (meth)acrylate and monocarboxylic or dicarboxylic acids,polyester resins formed from α-β-unsaturated dicarboxylic acids oranhydrides thereof and diols, urethane acrylates or polyepoxypolyacrylates.

Preferred compositions are those consisting of

(A) 80-99% by weight of a polymerisable compound having one or moreethylenically unsaturated bonds,

(B) 1 to 20% by weight of at least one aminoplast, such as amelamine-formaldehyde or ureaformaldehyde resin, and

(C) 0.1 to 10% by weight, based on the total of A and B, of a curingcatalyst of the formula I.

The lacquers can also contain minor amounts of special additives, suchas are customary in the technology of lacquers, for example flow controlassistants, thixotropic agents, light stabilisers, antioxidants orphotoinitiators.

Examples of light stabilisers are those belonging to the categorycomprising hydroxyphenylbenztriazoles, hydroxybenzophenones,cyanoacrylates, hydroxyphenyltriazines, oxalanilides, organic nickelcompounds or polyalkylpiperidine derivatives. Since light stabilisers ofthe UV absorber type can interfere with the UV irradiation according tothe invention, light stabilisers of this type can also be added to anadjacent lacquer layer, from which they then gradually diffuse into thelayer, to be protected, of stoving lacquer. The adjacent lacquer layercan be a primer under the stoving lacquer or a top lacquer over thestoving lacquer.

A further possible means of avoiding the disturbing effect of the UVabsorber consists in using so-called "blocked UV absorbers" such as aredescribed, for example, in German Offenlegungsschrift No. 2,648,367.Products which, in the course of a photo-Fries rearrangement form UVabsorbers, for example resorcinol monobenzoate or certain salicylic acidesters, are also suitable.

Polymethylpiperidine derivatives or combinations thereof with UVabsorbers are used preferentially.

The invention also relates to a process for curing acid-curable resinsin the presence of curing catalysts of the formula I or II byirradiation with shortwave light, followed by warming.

The irradiation of the resin with shortwave light is preferably effectedby means of UV light, for which there are nowadays a number of suitableindustrial devices. These contain medium-pressure, high-pressure orlow-pressure mercury vapour lamps and also fluorescent tubes havingemission maxima of 250 to 400 nm. The irradiation times required dependon the film thickness of the resin, on its pigmentation, on thecandle-power of the lamps and on the distance of the lamps. Anunpigmented lacquer in a customary layer thickness requires an exposuretime of a few seconds in conventional UV irradiation devices. The latentcatalyst has undergone photochemical transformation within this time,with the formation of free sulfonic acid.

If photosensitisers are added to the resin, the irradiation can also becarried out with daylight lamps. Examples of known photosensitisers arecondensed aromatic compounds, for example perylene, aromatic amines(such as are described, for example, in U.S. Pat. No. 4,069,054) orcationic and basic dyes (such as are described, for example, in U.S.Pat. No. 4,026,705).

Since the acid-curing takes place very slowly at room temperature, it isnecessary for carrying out the process industrially for the irradiationto be followed by a heat treatment. In contrast with other processesusing heat-cleavable curing catalysts, however, this can be carried outat relatively low temperatures. Stoving temperatures of about 70° to 80°C. are sufficient at a stoving time of about 30 minutes and if about 2%of catalyst are used. If 1% of catalyst is used, temperatures of about80° to 100° C. are required and, if 0.5% of catalyst is used,temperatures of about 100° to 120° C. are required. It is preferable tocure the resins catalysed in accordance with the invention attemperatures below 130° C., after irradiation. As against this, stovingtemperatures exceeding 130° C. are required for curing using known aminesalts of sulfonic acids (without irradiation).

These relatively low stoving temperatures of the process according tothe invention are of considerable industrial importance for coating orlacquering heat-sensitive substrates. Examples of these are articlesmade of wood or cardboard, but particularly articles containingcomponents made of plastics or rubbers, for example electricalequipment, vehicles of all kinds or machines.

A further advantage compared with other one-component resins containinga curing catalyst is that the one-component systems according to theinvention can be stored virtually indefinitely at room temperature,since the effective catalyst is only formed when irradiated.

The process according to the invention is suitable for all types ofindustrial coating and lacquering, for example for the lacquering ofmachinery, vehicles, ships or structural components. It is of particularimportance for automobile lacquering. In this field it can be employedin one-layer lacquering as well as in multi-layer lacquering. The use ofthe process is also of particular interest for the continuous coating ofsheet-metal, for example steel or aluminium sheet, by the so-calledcoil-coating process. The process is also suitable for curingacid-curable printing inks, which are particularly suitable fortin-printing because of their outstanding absorption capacity.

If the process according to the invention is used on moulding materials,casting resins and laminating resins, the resins can first be irradiatedin a thin film and then shaped under hot conditions to form any desiredarticles, and cured. If, however, articles of a relatively low thicknessare involved, the resins can also be shaped first and then irradiatedand heated. The film thickness used in the irradiation of the resins canbe several millimetres, depending on their transparency. The processfinds a further possible use in the production of relief forms, forexample printing plates. In this case the solid or liquid, acid-curableresin composition, which can also contain unsaturatedmonomers/prepolymers, is first effected through a negative film. This isfollowed, if desired, by a heat after-treatment, in which the exposedareas become crosslinked. Finally, the printing plate is developed bywashing out the non-crosslinked portions.

The examples which follow illustrate the process in greater detail byreference to specific compositions according to the invention. In these,parts are parts by weight and % are percentages by weight.

EXAMPLE 1 Curing a lacquer based on an acrylic-melamine resin.

Aluminium sheets 0.5 mm thick, which have been coated with awhite-pigmented priming lacquer based on a polyester resin, are coatedwith a high-solids clear lacquer of the following composition:

53.7 parts of acrylic resin (Paraloid® OL 42, Rohm & Haas Co., USA),

19.2 parts of melamine resin (Cymel® 301, American Cyanamide Co.),

1.9 parts of cellulose acetobutyrate (CAB® 551,001, Eastman Chem. Co.),

10.5 parts of n-butanol,

10.1 parts of butyl acetate,

2.9 parts of a flow control assistant (Byketol® Spezial,Byk-Mallinckrodt),

0.3 part of a flow control assistant (Modaflow®, Monsanto Company) and

0.63 part of a curing catalyst.

[Binder content, expressed as solids: 19.2 parts of melamine resin+42.96 parts of acrylic resin =62.16 parts]

The catalyst is previously dissolved in part of the butanol. The lacquerhas a solids content of 62.16 parts (binders). The amount of catalyst istherefore 1%, based on solvent-free binder.

The lacquer is applied with an electrical film applicator in such amanner that the dry film thickness is about 30 μm. After being exposedto the air for a period of 15 minutes, the samples are exposed to UVirradiation for varying periods in a PPG irradiation apparatus equippedwith 2 high-pressure mercury vapour lamps of 80 watt. The samples arethen stoved for 30 minutes at 100° C. in a lacquer oven.

The degree of curing is assessed by determining the pendulum hardness ofthe lacquer film by Konig's method (DIN 53,157); this is done 30 minutesand 24 hours after stoving.

The discoloration (yellowing) is assessed by determining the colourshade difference E as specified in DIN 6,174.

The results are listed in Table 1.

                  TABLE 1                                                         ______________________________________                                                    Irradi-                                                                       ation Pendulum hard-                                                                             Colour                                                     time  ness (seconds)                                                                             shade                                                      (sec- after:       difference                                     Catalyst      onds)   30 mins 24 hours                                                                             Δ E                                ______________________________________                                        1-Benzoyl-1-(methyl-                                                                        2,1     83       81    1,6                                      sulfonyl)-oxy-cyclo-                                                                        4,2     99      102    2,0                                      hexane        12,6    108     115    2,9                                      ______________________________________                                    

In addition, the stability on storage of the lacquer samples is checkedby measuring their viscosity with the ICI cone and plate viscometer (DIN53,229) during storage at 60° C. for 7 days.

In this method the viscosity is measured in poises. Table 2 shows thedifference (Δη) between the viscosity thus measured and the viscosity ofa catalyst-free sample of lacquer.

                  TABLE 2                                                         ______________________________________                                                   Difference in viscosity Δ η in                                      poises after storage at 60° C. for:                         Catalyst     0      1      2    3    4    7 days                              ______________________________________                                        1-Benzoyl-1-(methyl-                                                                       0.1    0.3    0.3  0.5  0.3  0.5                                 sulfonyl)-oxycyclo-                                                           hexane                                                                        ______________________________________                                    

EXAMPLE 2

The following base resin formulation is used as a basis

    ______________________________________                                                                Solids                                                ______________________________________                                        Hexamethoxymethylmelamine                                                                        17.93   g      17.93                                                                              parts                                  (Cymel ® 301, 100%)                                                       Butyl acetate      9.73    g                                                  Cellulose acetobutyrate                                                                          1.83    g                                                  (CAB ® 551,001, Eastman Chem.)                                            Silicone resin in an organic solvent                                                             2.80    g                                                  (flow control assistant Byketol ®                                         Spezial, Byk-Mallinckrodt)                                                    Flow control assistant having a                                                                  0.29    g                                                  polymer basis (Medaflow ®, 1%                                             solution; Monsanto)                                                           Hydroxyl-functional acrylic resin                                                                57.30   g      41.83                                                                              parts                                  (Paraloid ® AT 410, 73% by weight                                         Rohm & Haas)                                                                  n-Butanol          10.12   g                                                                     100.00  g      59.76                                                                              parts                                  ______________________________________                                    

The compounds listed in Table 3 are incorporated into this resinformulation in a concentration of 1% by weight (based on solvent-freebinder=59.76 parts). Testing is carried out as described in Example 1.The results are shown in Table 3. In this table, the stability onstorage at 60° of the lacquer samples is shown in terms of viscositymeasurements (viscosity is measured at 20° and quoted in poises).

                                      TABLE 3                                     __________________________________________________________________________                                               Colour                                                                              Stability after storage                                                       at                                                       Exposure                                                                           Pendulum hardness                                                                       shade 60° C., expressed                                                      as poises at                                             time,                                                                              in seconds after:                                                                       difference                                                                          20° C., after:        Catalyst                    seconds                                                                            30 mins.                                                                           24 hours                                                                           Δ.sub.E                                                                       0 1 2 3 4 7                  __________________________________________________________________________                                                               days                ##STR8##                    0 2.1 4.2 8.4 12.6                                                                 52 147 163 171 172                                                                 63 168 181 191 192                                                                0.2 0.5 0.7 1.3 1.8                                                                 3.1                                                                             4.0                                                                             5.2                                                                             6.8                                                                             8.0                                                                             11.2                ##STR9##                    0 2.1 4.2 8.4 12.6                                                                 18 148 174 183 183                                                                 17 154 187 196 196                                                                0.6 0.5 0.5 0.8 1.1                                                                 3.0                                                                             3.4                                                                             4.1                                                                             4.7                                                                             5.6                                                                              8.8               __________________________________________________________________________

EXAMPLE 3

Further lacquer films were prepared in accordance with Example 2, andtheir pendulum hardness as specified in DIN 53,157 was determined inorder to assess the degree of curing, and the colour shade difference ΔEas specified in DIN 6,174 was determined in order to assessdiscoloration/yellowing. The results are shown in Table 4.

                                      TABLE 4                                     __________________________________________________________________________                                                            Colour                                                              Pendulum hardness                                                                       shade                                                      Irradiation                                                                            in seconds                                                                              difference            Catalyst                             time (seconds)                                                                         30 mins                                                                            24 hours                                                                           ΔE              __________________________________________________________________________     ##STR10##                            0  2,1  4,2  8,4 12,6                                                                  19 128 166 179 179                                                                 21 136 181 195                                                                    0,5 0,2 0,2 0,1                                                               0,3                    ##STR11##                            0  2,1  4,2  8,4 12,6                                                                  22 132 168 179 182                                                                 27 143 183 194                                                                    0,5 0,1 0,2 0,4                                                               0,7                    ##STR12##                            0  2,1  4,2  8,4 12,6                                                                  39 179 189 188 179                                                                 42 191 197 202                                                                    0,4 0,2 0,1 0,1                                                               0,4                    ##STR13##                            0  2,1  4,2  8,4 12,6                                                                  25 127 167 182 185                                                                 29 137 182 199                                                                    0,5 0,2 0,1 0,2                                                               0,5                    ##STR14##                            0  2,1   7 106 151 169 171                                                                  8 117 169 189                                                                     0,3 0,1 0,5 0,6                                                               0,8                    ##STR15##                            0  2,1  4,2  8,4 12,6                                                                  8 175 176 179 177                                                                  10 191 193 197                                                                    0,3 0,3 0,6 1,3                                                               1,6                    ##STR16##                            0  2,1  4,2  8,4 12,6                                                                  11  69  99 136 154                                                                 11  73 104 148                                                                    0,2 0,2 0,3 0,9                                                               1,2                    ##STR17##                            0  2,1  4,2  8,4 12,6                                                                  31 136 164 177 177                                                                 34 145 181 193                                                                    0,2 0,4 0,4 0,6                                                               0,9                    ##STR18##                            0  2,1  4,2  8,4 12,6                                                                  11 174 179 182 183                                                                 15 191 197 196                                                                    0,3 0,6 0,8 1,3                                                               1,8                    ##STR19##                            0  2,1  4,2  8,4 12,6                                                                  21 143 165 175 176                                                                 24 155 181 190                                                                    0,1 0,3 0,5 0,5                                                               0,9                    ##STR20##                            0  2,1  4,2  8,4 12,6                                                                  8 123 164 182 183                                                                  11 128 178 195                                                                    0,3 0,2 0,4 0,7                                                               1,0                    ##STR21##                            0  2,1  4,2  8,4 12,6                                                                  7 165 171  178 178                                                                 8 183 189 192                                                                     0,3 0,3 0,5 1,0                                                               1,4                    ##STR22##                            0  2,1  4,2  8,4 12,6                                                                  26 182 183 183 184                                                                 22 187 192 197                                                                    0,6 0,5 0,6 0,8                                                               --                     ##STR23##                            0  2,1  4,2  8,4 12,6                                                                  15 138 171 181 183                                                                 15 140 183 196                                                                     0,3 0,4 0,6 1,1                                                              1,5                    ##STR24##                            0  2,1  4,2  8,4 12,6                                                                  14 166 181 185 184                                                                 13 178 193 196                                                                    0,4 0,4 0,5 0,9                                                               1,4                    ##STR25##                            0  2,1  4,2  8,4 12,6                                                                  46 173 184 187 186                                                                 49 180 194 188                                                                    0,2 0,3 0,4 0,8                                                               1,0                    ##STR26##                            0  2,1  4,2  8,4 12,6                                                                  41  68  99 150 168                                                                 39  64 102 151                                                                    0,1 0,1 0,3 0,7                                                               0,9                    ##STR27##                            0  2,1  4,2  8,4 12,6                                                                  17 146 174 183  183                                                                17 153 187 194                                                                    0,3 0,4 0,6 0,8                                                               1,1                    ##STR28##                            0  2,1  4,2  8,4 12,6                                                                  8 123 146 155 155                                                                  8 120 146 157                                                                     0,6 0,4 0,8 1,2                                                               1,4                    ##STR29##                            0  2,1  4,2  8,4 12,6                                                                  6 151 159 161 158                                                                  6 150 160 158                                                                     0,7 0,5 0,5 1,1                                                               1,5                    ##STR30##                            0  2,1  4,2  8,4 12,6                                                                  6 156 162 161 163                                                                  6 157 167 170                                                                     0,5 0,4 0,6 1,1                                                               1,4                    ##STR31##                            0  2,1  4,2  8,4 12,6                                                                  10 106 141 155 160                                                                 13  116 155 175                                                                   0,7 0,3 0,2 0,3                                                               0,7                   (contains 1 equivalent of CH.sub.3 OH)                                         ##STR32##                            0  2,1  4,2  8,4 12,6                                                                  56 150 172 178 182                                                                 64 165 187 193                                                                    0,5 0,2 0 0,2                                                                 0,5                    ##STR33##                            0  2,1  4,2  8,4 12,6                                                                  21   25  43  64 101                                                                    0,5 0,3 0,2 0                                                                 0,3                    ##STR34##                            0  2,1  4,2  8,4 12,6                                                                  10  91 131 155 160                                                                 10  94 138 170                                                                    0,1 0,3 0,4 0,5                                                               0,8                    ##STR35##                            0  2,1  4,2  8,4 12,6                                                                  7   65 106 144 157                                                                 7  66 111 155                                                                     0,1 0,1 0,5 0,6                                                               0,6                    ##STR36##                            0  2,1  4,2  8,4 12,6                                                                  14  68  92 115 123                                                                 13  68  92 118                                                                    0,1 0,4 0,5 0,5                                                               1,0                    ##STR37##                            0  2,1  4,2  8,4 12,6                                                                   20 173 184 176 185                                                                17 187 190 193                                                                    0,5 0,5 0,4 1,0                                                               1,5                    ##STR38##                            0  2,1  4,2  8,4 12,6                                                                  7  92 133 161 168                                                                  11 118 153 182                                                                    0,5 0,5 0,6 0,9                                                               1,2                   __________________________________________________________________________     *TOS = tosyl = ptolylsulfonyl                                            

EXAMPLE 4

Further lacquer films were prepared in accordance with Example 2, andtheir pendulum hardness as specified in DIN 53,157 was determined inorder to assess the degree of curing, and the colour shade difference ΔEas specified in DIN 6,174 was determined in order to assessdiscoloration/yellowing. The results are shown in Table 5.

                                      TABLE 5                                     __________________________________________________________________________                                          Colour                                                              Pendulum hardness                                                                       shade                                                       Irradiation                                                                           in seconds after:                                                                       differences                             Catalyst no.        time (seconds)                                                                        30 mins                                                                            24 hours                                                                           Δ.sub.E                           __________________________________________________________________________    5.1                                                                              ##STR39##         0 2.1 4.2 8.4 12.6                                                                    19  97 141 169 174                                                                 22 105 152 185 192                                                                0.3 0 0.1 0.5 0.8                       5.2                                                                              ##STR40##         2.1 4.2 8.4 12.6                                                                     113 154 175 182                                                                    106 147 167 182                                                                    0.7 0.6 1.0 1.2                         5.3                                                                              ##STR41##         0 2.1 4.2 8.4 12.6                                                                    9 140 169 175 178                                                                  14 156 185 192 197                                                                0.3 0.3 0.5 1.1 1.4                     __________________________________________________________________________     TOS = ptolylsulfonyl                                                     

If the benzoyl group in compounds Nos. 5.1, 5.2 and 5.3 listed in Table5 is replaced by a p-toluyl group, compounds are obtained which are alsovery suitable for use as curing catalysts and have test values similarto those listed in Table 5.

Similar test results are also given by the compound which was obtainedwhen the benzyl group in compound 5.1 was replaced by an isopropylgroup.

EXAMPLE 5

An imaging composition resin for relief forms is prepared by mixing thefollowing components:

25 parts of hydroxy-groups containing polyether (Desmophen® 550 fromBayer, Germany)

25 parts of hydroxy-groups containing polyester (Desmophen® 1100 fromBayer, Germany)

50 parts of melamine resin (Cymel® 301 from American Cyanamide Co., USA)

0,3 parts of a levelling agent (Byk® 300 from Byk-Mallinckrodt, Germany)

The curing catalyst is incorporated into this imaging composition resinin concentrations of 4% by weight and 6% by weight respectively.

The imaging composition prepared as above is applied to sheets ofaluminium (10×15 cm size and 200 μm thickness) in a thickness of 100 μm.A polyester sheet of a thickness of 76 μm is put on the liquid layer anda standardized testing negative with a 21 grey step tablet (Stoufferstep tablet) is put on said sheet. A second polyester sheet is put ontop and the laminate thus obtained is fixed on a metal sheet. Thesamples are then irradiated with a 5 KW-metal halogenide lamp from adistance of 30 cm for 20 seconds, 40 seconds and 60 secondsrespectively.

After the irradiation the polyester sheets and the testing negative areremoved and the irradiated layer is crosslinked by a heat-treatment of80° C. or 100° C. respectively for 30 minutes. Then the relief formplate is developed by washing out the non-crosslinked parts with ethanolin a supersonic bath for 10 seconds.

The sensitivity of the catalyst used is characterized by the number ofthe last step of the grey step tablet which is completely crosslinkedand has a tackfree surface. The higher the number of the step is themore sensitive is the catalyst. The results are given in Table 6

                                      TABLE 6                                     __________________________________________________________________________                                Catalyst-                                                                             Irradiation                                                                         Heat-treatment                                                  concentration                                                                         Time  temperature                                                                           Last step                   Catalyst                    [% by weight]                                                                         [seconds]                                                                           [°C.]                                                                          number                      __________________________________________________________________________     ##STR42##                  4 6     20 40 60 20 40 60 20 40 60 20 40                                                     80  80  80 100 100 100  80  80                                                80 100 100 100                                                                       3 5 7 4 6 7 4 5 7 4 7       __________________________________________________________________________                                                      9                       

What is claimed is:
 1. A process for the production of a relief imagewhich comprises(a) coating a substrate with a curable composition whichcomprises(1) an acid-curable resin which is an amino resin or a phenolicresin, or a mixture of an amino resin or a phenolic resin with an alkyd,polyester or acrylic resin, and (2) an effective amount of a curingcatalyst which is a compound of formula I or II ##STR43## in which n isthe number 1 or 2 and R₁ is phenyl or naphthyl which is unsubstituted orsubstituted by 1, 2 or 3 radicals belonging to the group comprising--Cl, --Br, --CN, --NO₂, C₁ -C₁₂ -alkyl, C₁ -C₄ -alkoxy, phenoxy,tolyloxy, phenylthio, tolylthio, C₁ -C₈ -alkylthio, --SCH₂ CH₂ OH, C₁-C₄ -alkylsulfonyl, phenylsulfonyl, C₂ -C₄ -alkoxycarbonyl, C₁ -C₄-alkylamino, C₂ -C₄ -dialkylamino, phenyl--CONH, C₁ -C₄ -alkyl--CONH--or benzoyl, or R₁ is also anthryl, phenanthryl, thienyl, pyridyl, furyl,indolyl or tetrahydronaphthyl, and R₂ is hydrogen or C₁ -C₈ -alkyl whichis unsubstituted or substituted by --OH, --Cl, C₁ -C₄ -alkoxy, --CN, C₂-C₅ -alkoxycarbonyl, phenyl, chlorophenyl, C₇ -C₁₀ -alkylphenyl or C₇-C₁₀ -alkoxyphenyl, or is also benzoyl, R₃ is as defined for R₂ and isalso phenyl which is unsubstituted or substituted by --Cl, C₁ -C₄-alkyl, C₁ -C₄ -alkoxy or C₁ -C₄ -alkylthio, C₂ -C₈ -alkoxycarbonyl,--CN, C₁ -C₄ -alkyl--NHCO--, phenyl--NHCO-- or --CONH₂, or R₂ and R₃,together with the carbon atom to which they are attached, constitute aC₄ -C₆ -cycloalkyl ring, X is --O--, --S--, --SO₂ --, --CH₂ --,--C(CH₃)-- or >N--COR₇, R₇ being C₁ -C₄ -alkyl or phenyl, and Y is adirect bond or --CH₂ --, and, if n=1, R₄ is C₁ -C₁₈ -alkyl, phenyl whichis unsubstituted or substituted by halogen, C₁ -C₁₂ -alkyl, C₁ -C₄-alkoxy, C₁ -C₄ -alkyl--CONH--, phenyl--CONH--, --NO₂ or benzoyl,naphthyl which is unsubstituted or substituted by halogen, C₁ -C₁₂-alklyl or C₁ -C₄ -alkoxy, C₅ -C₆ -cycloalkyl, C₇ -C₉ -aralkyl,camphoryl, --CF₃ ' --CCl₃, --F or --NH₂, and, if n=2, R₄ is a--(CH₂)_(m) -- group in which m is the number 2 to 8, or R₄ is phenyleneor naphthylene which is unsubstituted or substituted by C₁ -C₁₂ -alkyl,R₅ is H or 1, 2 or 3 radicals belonging to the group comprising --Cl,--Br, --NO₂, C₁ -C₁₂ -alkyl, C₁ -C₁₂ -alkoxy, phenoxy, phenylthio, C₁-C₈ -alkylthio or --SCH₂ CH₂ OH, and R₆ is hydrogen or C₁ -C₈ -alkylwhich is unsubstituted or substituted by --OH, --Cl, C₁ -C₄ -alkoxy,--CN, C₂ -C₅ -alkoxycarbonyl, phenyl, chlorophenyl, C₇ -C₁₀ -alkylphenylor C₇ -C₁₀ -alkoxyphenyl, phenyl which is unsubstituted or substitutedby --Cl, C₁ -C₄ -alkyl, C₁ -C₄ -alkoxy or C₁ -C₄ -alkylthio, C₂ -C₈-alkoxycarbonyl or --CN, (b) irradiating said coating through a negativefilm with short-wave light, c) heating the coating to crosslink theareas of the coating exposed to irradiation, and (d) developing therelief image by washing out the non-crosslinked portions with adeveloper solvent.